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Mn-doped TiO2 nanorods which showed room temperature ferromagnetic (RTFM) behavior have been synthesized by a hydrothermal method. Analysis of X-ray diffraction and Raman spectral data reveal the formation of anatase phase without any impurity phase. From the hysteresis loop measurements, it is possible to estimate the two parameters, magnetization (MS) and coercivity (HC) which are 33 memu/g and 89 Oe respectively, for 5 at% Mn-doped TiO2. The two parameters (MS, HC) are strongly dependent on the Mn doping concentration. The origin of the RTFM is understood in terms of the concentration of oxygen vacancies and/or defects which is created by Mn doping.

Dye-doped deoxyribonucleic acid-surfactant films have been prepared by an intercalation method and their optical properties have been investigated. Coumarin 1 (C1), known as a neutral laser dye, can be successfully incorporated in deoxyribonucleic acid-surfactant films by immersing them in aqueous dye solution. About 6 wt% C1 can be doped in samples when the immersion time is 86400 s. C1-doped samples show pronounced optical absorption and photoluminescence bands. Not only hydrophobic-hydrophobic interactions but also molecular structures of dyes play prominent roles in the formation of neutral dye-doped deoxyribonucleic acid-surfactant films. It is surmised that C1 stays inside the double helix of deoxyribonucleic acid (DNA) and/or between the alkyl groups of surfactants.

Zinc oxide in the bulk as well as in the nanocrystalline form is thermodynamically stable in the wurtzite structure. However, zinc oxide in the zinc-blende structure is more useful than that in the wurtzite structure due to its superior electronic properties as well as possibility of efficient doping. Therefore, zinc oxide shell is grown epitaxially on zinc sulphide core nanoparticles having zinc-blende structure. It is shown that doping of manganese could be achieved in zinc oxide nanoshell with zinc-blende structure.

Magnetic nanoparticles of iron oxide were synthesized by transferred arc plasma induced gas phase condensation method. Structural, morphological and magnetic studies of the as synthesized powder were carried out using X-ray diffraction, transmission electron microscopy and Mossbauer spectroscopy. These studies have revealed the simultaneous nucleation and condensation of different magnetic phases with a broad size distribution of the nanoparticles which is peaked at 30–50 nm and ranges from 10 nm to 80 nm. 57Fe Mossbauer spectra recorded at various temperatures (5 K–300 K) in presence of external magnetic field (at 5 K) have suggested the presence of different phases of iron oxide with sizable amounts of γ-Fe2O3 and α-Fe2O3 in addition to Fe3O4. The relative concentrations of these phases have been obtained by a self consistent spectral area analysis and were found to be 44:22:34 (%).

The concentration on Cu 2 O (Cu 2 O=1, 2, 3 and 4 wt.%) powder-dependent gas-sensing performance of δ-Al 2 O 3 /Cu 2 O material screen-printed on α-Al 2 O 3 substrates and heated at 750 °C/1 h is evaluated systematically. For this purpose, nanocrystalline δ-Al 2 O 3 (15–20 nm) powder prepared by DC IS plasma technique was used as a functional material. Resultant δ-Al 2 O 3 /Cu 2 O samples were characterized by XRD, scanning electron photomicrograph (SEM) and Half bridge method. The characterization studies revealed that the sensitivity factor (SF) decreases with increase in additive weight percentage of Cu 2 O for all the three gases of CO, H 2 and LPG. It shows maximum SF of 165, 296 and 78 for CO, H 2 and LPG gases (1000 ppm each), respectively, at an optimum operating temperature ( T opt. ) of 450 °C for 1 wt.% of Cu 2 O. All the gases show flat response for all concentration values of Cu 2 O at the above 2 wt.%. Thus, the present material (δ-Al 2 O 3 /Cu 2 O, Cu 2 O=1 wt.%) shows more selectivity for H 2 gas over LPG compared to CO ( S H 2 / S CO =1.8 and S H 2 / S LPG =4.3). The particle size of δ-Al 2 O 3 /Cu 2 O samples was found to be in the range of 0.05–0.5 μm.

Synthesis of La 0.5 Ba 0.5 MnO 3 powder by microwave-hydrothermal (MH) accelerated solid state reaction (SSR) route is reported. In this method, SSR is accelerated by use of MH route. MH route decreases the formation temperature to 900 °C and reaction time to 8 h when compared to 1400 °C and 48 h, respectively, for conventional solid state reaction method. The materials are characterized by powder XRD, SEM, TEM, temperature dependence of AC susceptibility and four-probe magnetoresistance technique in a magnetic field of 1 T. XRD data show the formation of the desired phase without any secondary phases. SEM studies reveal agglomeration nature of primary particles with agglomerate size ∼1 μm and the TEM picture supports SEM analysis. AC susceptibility, resistivity in the absence of magnetic field ( ρ 0 ) and in the presence of the field ( ρ H ) and magnetoresistance: MR=[( ρ 0 − ρ H )/ ρ 0 ] all show a peak or a small structure at ∼200 K indicative of a magnetic phase transition at this temperature.

The effect of variation of sintering temperature (600–800 °C/4 h) on the gas sensing characteristics of a SnO 2 :Cu (Cu=9 wt.%) system (a high-performance temperature-selective composition) in the form of pellets is investigated systematically for the CO, H 2 and LPG gases at a concentration level of 1000 ppm. The XRD, SEM and half-bridge techniques were employed to establish the structural, morphological and gas sensing characteristics of the materials, respectively. A very high value of sensitivity factor (SF) equal to 1400 is obtained for CO gas at an optimal operating temperature of 160 °C for the pellets sintered at 750 °C. The selectivity values of CO gas against H 2 and LPG ( S CO / S H 2 ∼14 and S CO / S LPG ∼280) at an optimum temperature of 160 °C are also improved considerably. This material (SnO 2 :Cu, Cu=9 wt.% sintered at 750 °C with an optimal temperature of 160 °C) may prove to have tremendous potential for CO gas sensing applications.

Systematic evaluation of gas-sensing characteristics of Cu-modified SnO 2 pellets for CO, H 2 and CH 4 gases from ppm to percentage level is reported. The concentration level of Cu additive was varied systematically from 1 to 11 wt %. The highest values of sensitivity factor (SF) of 240 and 590 corresponding to CO and H 2 gases were obtained at considerably lower temperatures of 160 and 230 °C, respectively, for 9 wt.% of Cu. The selectivity values are found to be maximum at 7 and 9 wt.% of Cu for H 2 (≈78) and CO (≈1.9) gasses, respectively. For CH 4 gas, on the contrary, the sensor showed quite inferior response. The sensitivity curve for our material follows the usual trend of three-region behaviour of standard Windischmann and Mark's curve. The sensor tends to saturate at 1.5% and 3.6% for CO and H 2 , respectively. XRD and scanning electron micrograph (SEM) characterisation techniques are used to pinpoint the possible reasons for high performance of the sensor at 9 wt.% Cu. Our sensor material showed promising properties for gas-sensing (CO and H 2 ) applications.

Barium–strontium titanyl oxalate (BSTO) [Ba 1− x Sr x TiO(C 2 O 4 ) 2 ·4H 2 O with x =0.25 precursor powders] were prepared successfully by using the simple chemical exchange reaction between oxalotitanic acid (HTO) [H 2 TiO(C 2 O 4 ) 2 ·2H 2 O], barium hydroxide and strontium nitrate at room temperature. Initially, oxalotitanic acid was prepared by using the reaction between 0.1 M titanium tetrabutoxide and 0.2 M oxalic acid in isopropanol (IPA). Barium hydroxide and strontium nitrate were added directly to this solution in stoichiometric amounts. The required solubility achieved only after addition of distilled water dropwise leads to the controlled precipitation of BSTO molecular precursor. To maintain the equilibrium (pH conditions), more and more Ba(OH) 2 and Sr(NO 3 ) 2 solids get dissolved and reaction continues. The kinetics of exchange reaction is governed by the rate of addition of water. The pyrolysis of BSTO at 750 °C/4 h in air produced the Ba 1− x Sr x TiO 3 (BST) powders. The characterization studies were carried on the as-dried and calcined powders by various physicochemical techniques viz. microanalysis, chemical analysis, DTA/TGA, XRD, IR, scanning electron microscopy (SEM), etc. It revealed that the BST powders are cubic, stoichiometric, highly pure with yield>99% and agglomerated nature (size: 0.5–2 μm).

The GNP route has been successfully employed to generate nanosized, porous, stoichiometric, homogeneous Ce0.75Zr0.25O2 powders. In this route, a precursor solution is prepared by mixing glycine with an aqueous solution of mixed (Ce–Zr) metal–nitrates in their stoichiometric ratios. Initially, the glycine mixed precursor solution was heated in a petri dish to evaporate the excess water to form a viscous semitransparent material. Then the petri dish was kept in a 5-l capacity beaker covered with a metallic mesh and then the temperature was increased slowly to 190–200 °C to autoignite the material. The combustion was self-sustaining and very rapid, producing yellowish coloured powders. The as-prepared powders were nanosized (20–35 nm), having a spherical shape, and were crystallized in cubic fluorite structure with lattice parameter a0=5.38 A. The powders showed a very wide pore size distribution in the range of 20–2500 A as is shown by mercury porosimetry measurements with surface area ≈40.0 m2/g. No change in crystalline phase was observed even after giving heat treatments to as-prepared powders up to 1000 °C for 4 h in air .The SEM/TEM studies on these powders confirmed their nanosized nature with porous structure.

Submicron-sized (0.15–0.2 μm) spherical agglomerates of magnetite (Fe3O4) powders have been prepared successfully by microwave hydrothermal (MH) reaction of ferrous sulphate and sodium hydroxide in the temperature range of 90–200 °C. X-ray powder diffraction patterns of all these powders indicated that the product is single-phase magnetite with cubic spinel structure having lattice parameter, a0=8.392 A. The Mossbauer spectra of these powders indicated that stoichiometric Fe3O4 particles are obtained only when molar ratio of Fe/NaOH≥0.133 is maintained in the solution. It is observed that Fe/NaOH ratio is an important parameter for the controlled oxidation of ferrous salts in alkaline media under MH condition to produce stoichiometric Fe3O4. Further, the kinetics of MH synthesis is one order faster than the reported conventional hydrothermal (CH) synthesis. The value of saturation magnetization M=70 emu/g is obtained in case of stoichiometric Fe3O4. However, when ferric salt is treated in alkaline medium single-phase α-Fe2O3 is obtained under the MH conditions of 200 °C (194 psi).

A chemical co-precipitation route is developed to precipitate mixed oxalates (PbC 2 O 4 +TiOC 2 O 4 .2H 2 O) at room temperature. In this synthesis route, an anionic TiO(C 2 O 4 ) 2 −2 species obtained by dissolving potassium titanyl oxalate (KTO) (0.01 M) stable over narrow pH range are destabilized with the addition of 0.01 M solution of lead chloride (PbCl 2 ) to produce insoluble TiOC 2 O 4 .2H 2 O and oxalic acid. The in situ generated oxalic acid during destabilization process reacts with Pb 2+ ions to precipitate lead oxalate (PbC 2 O 4 ). The mixed oxalates on pyrolysis in air at 750 °C/4 h produced submicron sized (0.13–0.15 μm) stoichiometric PbTiO 3 (PT) powders having tetragonal symmetry (with c / a ratio ∼1.063) which form agglomerates of size 0.5–5 μm. Various physico-chemical techniques were used to characterize the as-dried mixed oxalates precursor and PbTiO 3 powders . All these experimental results related to synthesis and characterization of these powders are presented in this paper.

A self-sustaining controlled acid–base reaction between oxalotitanic acid [H2TiO(C2O4)2] (HTO) and barium hydroxide [Ba(OH)2� 8H2O] at room temperature is utilized for the quantitative precipitation of barium titanyl oxalate (BTO). For this purpose, an intermediate soluble oxalotitanic acid precursor is generated by reacting 0.1 M solution of titanium tetrabutoxide in isopropanol (IPA) with 0.2 M solution of oxalic acid in IPA. Equimolar suspended Ba(OH)2 particles in IPAwere mixed with the above-mentioned oxalotitanic acid solution. The self-sustaining acid–base reaction between Ba(OH)2 and H2TiO(C2O4)2 was initiated only when necessary amount of water was added. This shift from non-aqueous to semi-aqueous condition allows a required solubility of Ba(OH)2, which makes Ba 2+ ions available for the exchange reaction. The solubility of Ba(OH)2 and its dissociation governs the kinetics of the reaction leading to the precipitation of BTO with yield z99%. The controlled pyrolysis of BTO at 750 jC/4 h in air-produced agglomerated cubic BaTiO3 powders having spherical particles with size c100 nm. These powders are sintered in the form of pellets at 1300 jC/4 h to obtain compacts with density c95%. These compacts showed dielectric constant eRT=1680 (tandV2%), emaxc7780 at TC=121 jC. D 2002 Elsevier Science B.V. All rights reserved.

An improved chemical route is described to precipitate quantitatively a molecular precursor lead zirconyl oxalate tetrahydrate, PbZrO(C 2 O 4 ) 2 ·4H 2 O (PZO) at room temperature. In this route, soluble ammonium zirconyl oxalate, (NH 4 ) 2 ZrO(C 2 O 4 ) 2 (AZO), is initially prepared by chemical reaction of 0.1-M solution of zirconyl nitrate with 0.2-M solution of ammonium oxalate. The anionic species ZrO(C 2 O 4 ) 2 −2 thus obtained is exchanged by adding equimolar solution of lead acetate to precipitate single-phase PZO with higher yield. The improvement in the presently described route is to drive exchange reaction to its completion by suitably manoeuvring the choice of precursor, pH and reaction conditions, in such a way that single-phase PZO is precipitated without any destabilization of anionic species ZrO(C 2 O 4 ) 2 −2 . The pyrolysis of PZO produced stoichiometric, monophasic, orthorhombic PbZrO 3 (PZ) powders at temperature T =700°C. Various physico-chemical techniques were used to characterize both molecular precursor PZO as well as PZ powders obtained by its pyrolysis. All our experimental results related to the synthesis and characterization of these powders are presented in this paper.

Two different ferromagnetic phases of the perovskites RMn 0.5 Co 0.5 O 3 (R=Pr, Nd, Sm) have been synthesized in single phase forms by a low-temperature method. For each compound, a phase with a higher ferromagnetic transition temperature is obtained for samples heated at 700°C, whereas a second phase having a lower ferromagnetic transition temperature is obtained for samples heated at 1350°C. Samples heated in the temperature range 700–1350°C showed mixed phase behavior.

Neutron depolarization ( P ), diffraction and magnetization measurements were carried out for a cluster glass compound La 0.5 Sr 0.5 CoO 3 . Below T ∼240 K significant depolarization is observed indicating the ferromagnetic transition. The temperature dependence of P appears to be correlated with the coercive field, H C . Difference between P in zero-field-cooled and field-cooled state is found below ∼225 K. The various features are compared with normal ferromagnet and reentrant spin-glass.

Polycrystalline single phasic mixed ferrites belonging to the series Ni1−xZnxFe2O4 for various values of x have been prepared by conventional ceramic techniques. Pre-characterized nickel zinc ferrites were then incorporated into a natural rubber matrix according to a specific recipe for various loadings. The processability and cure parameters were then determined. The magnetic properties of the ceramic filler as well as the ferrite loaded rubber ferrite composites (RFC) were evaluated and compared. A general equation for predicting the magnetic properties was also formulated. The validity of these equations were then checked and correlated with the experimental data. The coercivity of the RFCs almost resemble that of the ceramic component in the RFC. Percolation threshold is not reached for a maximum loading of 120 phr (parts per hundred rubber by weight) of the filler. These studies indicate that flexible magnets can be made with appropriate magnetic properties namely saturation magnetisation (Ms) and magnetic field strength (Hc) by a judicious choice of x and a corresponding loading. These studies also suggest that there is no possible interaction between the filler and the matrix at least at the macroscopic level. The formulated equation will aid in synthesizing RFCs with predetermined magnetic properties.

Rubber ferrite composites containing various mixed ferrites were prepared for different compositions and various loadings. The magnetic and dielectric properties of the fillers as well as the ferrite filled matrixes were evaluated separately. The results are correlated. Simple equations are proposed to predetermine the magnetic and dielectric properties. The validity of these equations is verified and they are found to be in good agreement. These equations are useful in tailoring the magnetic and dielectric properties of these composites with predetermined properties.

A new combustion route for the synthesis of γ-Fe 2 O 3 is reported by employing purified a-Fe 2 O 3 as a precursor in the present investigation. This synthesis which is similar to a self propagation combustion reaction, involves fewer steps, a shorter overall processing time, is a low energy reaction without the need of any explosives, and also the reaction is completed in a single step yielding magnetic iron oxide i.e. γ-Fe 2 O 3 .The as synthesized γ-Fe 2 O 3 is characterized employing thermal, XRD, SEM, magnetic hysteresis, and density measurements. The effect of ball-milling on magnetic properties is also presented.

Two distinct single phases of ferromagnetic LaMn 0.5 Co 0.5 O 3 have been synthesized by the low-temperature glycine-nitrate method. Sample heated to 700°C shows a single well-defined ferromagnetic transition at T c ≈225 K whereas the sample heated to 1300°C shows a sharp ferromagnetic transition at T c ≈150 K. Mixed phase behavior is observed for samples heated in the temperature range 700–1300°C.

Controlled chemical precipitation method was used to obtain nanosized titania (TiO2) powders. XRD, DTA/TGA/DTG techniques were employed for phase analysis and to know the thermal changes taking place in precipitated precursor during heating. The effect of processing and fabrication conditions viz. calcination temperature, mold pressure and sintering temperature/time on membranes prepared from this titania powder was studied using permeability measurements. The bulk porosity, average pore size and permeability were found to decrease with increase in the molding pressure. However, an increase in the sintering period increases the bubble point and brings the diameter of the larger pores nearer to that of the average pore.

Nanoparticles of zinc sulphide have been synthesized by a chemical method. Mercaptoethanol is used to passivate the surface of the particles. Under certain conditions highly luminescent particles emitting blue light at ∼425 nm can be synthesized. This blue light emission in nanoparticles of zinc sulphide is observed to be completely quenched when doped with iron or nickel metal ions.

Polycrystalline nickel-zinc ferrite powder was obtained by chemical coprecipitation involving the corresponding metal nitrates and sodium hydroxide. The precipitate, when dried at 80 °C in air, was characterized by powder XRD, SEM and VSM measurements. It shows the formation of cubic ferrite with saturation magnetization M s ≈ 44 emu / g . When calcined at 1200 °C, the magnetization reached 96% of the saturation value, M s ≈ 67 emu / g . The temperature dependence of magnetization confirmed the Curie temperature T c ≈ 480 ° C.

When tin oxide is doped with Sb2O3 and CoO, it shows highly nonlinear current (I)-voltage (V) characteristics. Addition of CoO leads to creation of oxygen vacancies and helps in sintering of SnO2. Antimony oxide acts as a donor and increases the conductivity. The results are nearly the same when antimony oxide is replaced by tantalum oxide. The observed nonlinear coefficient, α = 30 and the breakdown voltage is 120 V/mm.

A novel chemical passivation route is established to obtain microcrystalline solid solutions of binary oxide system Mn1−x Ni x O (0·01

A new aqueous metallo-organic precursor, namely, lead lanthanum zirconyl titanyl oxalate (PLZTO) has been developed using complexes of Pb 2+ , La 3+ , Zr 4+ and Ti 4+ with required stoichiometry. Controlled pyrolysis of the PLZTO precursor at sufficiently low temperatures ( T ≈ 525° C ) in air resulted in cubic powders of lead lanthanum zirconate titanate (PLZT). Thermal analysis (DTA/TG/DTG), X-ray diffraction (XRD), micro- and chemical analysis, X-ray fluorescence (XRF) and IR studies were used to characterize the precursor and resulting PLZT powder. The dielectric ( K , tan δ) and ferroelectric ( P s , E C ) properties of the sintered compacts were measured at room temperature.

Small quantities of rare earth element such as La or Y were incorporated into the SnO 2 -based primitive varistor compositions. This leads to increase in nonlinear coefficient, α from 9 to 30 and the breakdown voltage increases from 120 to 220 V/mm. The enhancement in α was expected to arise from the possible segregation of lanthanide ion due to its larger ionic radius to the grain boundaries, thereby modifying its electrical characteristics. Furthermore, the dopants such as La may help in adsorption of O′ and O″ at the grain boundaries [J. Appl. Phys. 84 (1998) 3700], thereby improving grain boundary barrier characteristics.

The solid solutions of Sn1−x Ti x O2 (0.0

Ultrasonic testing is useful for detecting plastic-metal debonding in an IC package. A positive phase echo relative to an input pulse is received from the bond region, whereas a negative phase echo is received from the debonding region because of the difference of acoustic impedance between the plastic and metal in the IC package. The purpose of this study is to examine the change from the positive to the negative echo with a small air gap in this solid-solid boundary. In these experiments, we used a gage block which is made of steel and has a flat surface for micrometer calibration, and a convex lens which is for a Newton ring experiment. as a test specimen. This specimen has a small air gap changing from actual contact with zero space to a gap space of order of microns.Ultrasonic immersion testing was carried out using 5MHz and 25MHz probes. The change of echo height and echo phase with gap space was examined. And then, we could simulate the change of waveform during the transition by mixing tw...

Ultrafine (≍0.4 μm) strontium titanate powder was synthesized using strontium nitrate and potassium titanyl oxalate as precursors. An aqueous (0.1 M) potassium titanyl oxalate solution was added dropwise to a (0.1 M) strontium nitrate solution with continuous stirring at room temperature to precipitate strontium titanyl oxalate (STO). The precipitate, after careful washing with distilled water several times, was air-dried and calcined at 550 °C/6 h to obtain homogeneous, spherical, stoichiometric powder of SrTiO3 ≍0.4 μm in size. The calcined powder was characterized using different techniques such as XRD, DTA/TG/DTG, SEM, and IR.

Barium carbonate with glacial acetic acid and butyl titanate monomer (BTM) were used as Ba and Ti precursors to obtain sols and hard transparent gels at room temperature. After the calcination of the gels at various temperatures (25–1250°C) in air, the mixed Ba Ti powder was characterized by DTA/DTG/TG, XRD and IR. The formation of tetragonal BaTiO3 as a major phase was seen to occur around 550°C.

A novel method of preparation, involving careful formation of a stoichiometric solid solution of stabilized Mn1-x Mg x O system for eight different concentrations ofx (0.001 ⩽x ⩽ 0.15) is described. A variety of physicochemical techniques such as X-ray diffraction, DTA-TGA, reflectance spectra, magnetic susceptibility and XPS data are used to determine structure-property correlations in the solid solutions, which are (i) X-ray diffraction studies reveal the linear decrease of cubic lattice parameter with increasing x, (ii) DTA-TG-DTG studies which confirm the formation of solid solution and the stability of these solid solutions in air which increases from 515 to 565 K withx, (iii) the diffused reflectance spectra shows nearly perfect octahedral symmetry around Mn2+ ions, (iv) magnetic susceptibility data indicates the usual dilution effects of diamagnetic ions in antiferromagnetic host lattice, (v) XPS studies reveal the presence of mixed phase of Mn2O3-MgO on the surface which protects the bulk MnO from its further oxidation to higher oxides of manganese. This shows the important role of Mg2+ in the chemical passivation of manganous oxide.

Nano size (< 200 nm) barium titanate was synthesized using barium acetate and potassium titanyl oxalate as precursors. Aqueous (0.01 M) potassium titanyl oxalate was added dropwise to a 0.01 M aqueous barium acetate solution with continuous stirring at room temperature to precipitate barium titanyl oxalate (BTO). The precipitate, after careful washing with distilled water several times, was dried in an oven at 70°C and calcined in air at 550°C/6 h to produce spherical, homogeneous, stoichiometric powder of BaTiO3 < 200 nm in size. The calcined powder was characterized using different techniques such as XRD, DTA/ TG/DTG, SEM/TEM and IR techniques.

The liquid-mix technique is used to prepare 4–24 mole% lanthana-zirconia cubic solid solutions (stabilized) at temperatures of about 800°C. Various physico-chemical techniques such as powder X-ray diffraction, infrared, electron microscopy, electron paramagnetic resonance, differential thermal analysis and X-ray photoelectron spectroscopy, have been employed to confirm phase formation, thermal stability and microstructure.

Thin films of lead titanate (PbTiO 3 ) on alumina and quartz substrates were obtained using sodium plumbate and titanium tetrachloride as precursors. The experimental work involves 1. (i) the reaction of vapours of titanium tetrachloride (TiCl 4 ) with a sodium plumbate (Na 2 PbO 2 ) aqueous solution to form a thin film directly at the interface 2. (ii) subsequent heat treatment of the as-deposited film, collected on the alumina and quartz substrates, at around 310°C in air, to obtain stoichiometric PbTiO 3 films. These films were characterised using X-ray fluorescence (XRF), thermogravimetric analysis (DTA/TG/DTG), X-ray diffraction (XRD), infrared (IR) and X-ray photoelectron spectroscopy (XPS) techniques.

A new varistor composition based on SnO2 doped with Co, Al, and Nb has been successfully synthesized by a chemical route. It exhibits excellent nonlinear current-voltage (I-V) characteristics with α ≈ 72 and E1mA ≈ 1820 V/mm.

A new ceramic voltage sensor based on SnO2 doped with Co, Nb and Al has been successfully synthesized by ceramic route. The ceramic compact exhibited excellent non-linear current-voltage (I-V) characteristics withα ≈ 24 andE 1mA ≈ 700 V/mm.

A molecular precursor barium zirconyl oxalate (BZO) was synthesized by exchange reaction between freshly generated water soluble sodium zirconyl oxalate and Ba-nitrate solutions at room temperature. The controlled pyrolysis of BZO in air at 800 °C/6 h resulted in the formation of single-phase cubic microcrystalline barium zirconate powder. These powders exhibit variable-shaped agglomerates with an average size ≍0.2 μm having a surface area ≍2.63 m2/gm.

Temperature dependence of the electrical resistivity of La 1−x Ca x MnO 3 (x = 0.2, 0.3) samples sintered at two different temperatures are compared to understand the origin of the double-maxima-type resistivity curves of some doped perovskite manganates reported in the literature. It is shown that compositional inhomogeneity is responsible for the anomalous electrical properties of the substituted manganate samples processed at low temperatures.

A simple coprecipitation technique is described for the preparation of tin substituted zirconium titanate ceramic powders.

Highly uniform submicrometre size particles of hexagonal strontium ferrite (SrFe12O19) have been synthesized by chemical coprecipitation technique at pH ⋍ 13. Chemical coprecipitation technique has helped in bringing down the ferritization temperature from 1300 to 925° C which is revealed by DTA-TG and XRD studies. Reproducible uniform single domain particle size and its distribution has been observed by scanning electron microscopy. X-ray and Mossbauer studies have identified single phase ferrite with Fe3+ ions occupying the proper crystallographic sites. The performance parameters of the sintered isotropic strontium ferrite magnets have proved to be superior by about 20% over the ferrites prepared by conventional ceramic technique.

Thick films of cadmium oxide were obtained by screen printing and firing in the temperature range 873–1173 K for 10 min. Scanning electron micrographs of the films showed the increasing grain growth with firing temperature. The relative grain size was estimated using the X-ray diffractograms of these films. The variation of relative grain size with temperature gave an activation energy of 125 ± 11 kJ/mol.

The magnetic behaviour of two ferromagnetic oxides and two ferrimagnetic oxides (ferrites) are compared to study the effect of magnetocrystalline anisotropy on thermal-history-dependence of magnetization of these ordered magnetic systems. All four compounds show thermomagnetic irreversibility (M FC >M ZFC) below a certain temperature,T irr. The highly anisotropic ferromagnetic oxide, SrRuO3 and the hard ferrite, SrFe12O19 show sharp peaks belowT c in theirM ZFC(T) curves, whereas for the soft ferrite Ni0.8Zn0.2Fe2O4 and the low anisotropic ferromagnetic oxide La0.7Ca0.3MnO3 only a broad maximum is observed inM ZFC, when measured in small magnetic fields. The shapes of theM ZFC(T) curves are inversely-related to the magnitude of the coercivities (H c) of the compounds in relation to the applied field, and the temperature dependence of Hc.M FC andM ZFC are related through the coercivity for all four magnetic systems.